When you first sign up for Beastkeeper you get a free 2 week Premium-subscription, to see what it's all about and if you like it. If you wish to continue having it after this trial period has ended, you will need to spend some gold coins on it or buy the item 1 Month Premium Subscription from other players through Item Exchange or Auction House.
What's included is in the FAQ under Premium Membership and Gold Coins Questions:
- Premium users can set Triggers.
- Premium users see maneuvers that are currently selected by your opponents at the Battlefield.
- Premium users get Inbreeding Warning when trying to breed pets that are close relatives.
- Normal users can perform searches only among pets which are being traded. Premium users can search among all pets. This can be useful if you're looking for a pet with special traits and want to buy it from another Keeper who didn't put this pet up for trade.
- Normal users only see a pet's mother and father. Premium users have access to full genealogy.
- Premium users can instantly leave the island from any point of the map. Normal users need to move to the portal tile frst.
How to get gold coins is also covered in the FAQ. I would suggest reading the entirety of it anyway, as there are many important informations in there :)